Dryer control



Sept. 24, 1968 I HETRICK 3,402,478

DRYER CONTROL Filed June 20, 1966 i 5 Sheets-Sheet l WITNESSES INVENTORW14 fW George L. Hetrick J W; fi AGENT Se t. 24, 1968 G. L. HETRICKDRYER CONTROL Filed June 20, 1966 5 Sheets-Sheet 2 LOW HEAT NO HEAT 0REGULAR HEAT P 1968. G. L. HETRICK 3,402,478

DRYER CONTROL Filed June 20, 1966 5 Sheets-Sheet 5 samba OF A M Y Q AAll VOLTAGE DRUP ACROSS ELECTRODES OF TIME /0 OF CONTACT TIME OF MOISTPARTS OF LOAD TO SENSOR INTEGRATING TiMER RUNOUT TIME TIME

United States Patent 3,402,478 DRYER CONTROL George L. Hetrick,Washington Township, Mansfield, Ohio, assignor to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed June20, 1966, Ser. No. 558,951 8 Claims. (CI. 3453) ABSTRACT OF THEDISCLOSURE An automatic timer for a clothes dryer which includes asensing portion which generates signals representative of moisturecontent in the clothes as a function of electrical conductivitytherethrough. The timer is characterized in that the signals generatedare manifested as a mechanical displacement of a conventional camrotated by a conventional timer motor, accordingly, there is anelectromechanical integration of the electrical signals generated.

This invention relates, in general, to clothes dryers and moreparticularly to an automatic or moisture sensing timer control for usetherewith.

Clothes drying apparatus at an early date, utilized timers that could bemanually set in order to establish the duration of the drying cycle soas to accommodate the drying of different size loads of clothes todifferent degrees of dryness, as desired by the user.

While such an arrangement is reasonably satisfactory, the end result isdependent upon the judgment of the operator with respect to his or herestimate as to the time required to dry the particular load of clothesto the desired degree of dryness. The use of many mechanical aids, forexample, weighing scales, have been suggested and tried in order tobetter establish this estimate, the result being only to reduce thelimits of error of the unaided estimate, however, not the totalelimination of the error.

Many principles and related constructions have been tried to overcomethe forging problem. All approaches appear to have paved the way for thelatest principle which is based on the measurement of moisture contentremaining in the clothes as a function of electrical conductivity orresistance. One of the first and probably the most typical controls ofthis type utilizes a moisture sensor in conjunction with anelectromechanical timer motor which advances a cam between on and offpositions. The moisture sensor provides an electrical signal whichtriggers means for starting the timer motor. With such an arrangementthe run-out time of the timer motor and cam represents a fixed amount ofquantity, therefore the timer motor must be calibrated such that thelargest load will be completely dried. This, as will be obvious,presents a problem of overdrying where it is desired to dry a relativelysmall load of clothes utilizing such a control.

Accordingly, it is the general object of this invention to provide a newand improved automatic moisture sensing control for clothes or fabricdryers.

It is a more particular object of this invention to provide a new andimproved automatic moisture sensing control for clothes dryers whereinvarying electrical signals generated in the dryer basket aremechanically integrated by means of a conventional timer motor.

Another object of this invention is to provide a new and improvedautomatic moisture sensing control for clothes dryers comprising anelectromechanical motor, the run-out time of which is a function of bothmoisture content in the clothes and the contact time of sensingelectrodes by the moist portions of the clothes.

A further object of this invention is to provide a new "ice and improvedclothes dryer control, the run-out time of which, for the purpose ofdamp drying, may be either a function of variable time or variableresistance.

Briefly, the present invention accomplishes the abovecited objects byproviding mechanical integrating means in the form of a conventionalclothes dryer timer motor and associated cam structure for integratingor storing electrical signals generated in a clothes dryer basket bymeans of electrodes bridged by wet clothes contained in the basket. Thesignals are indicative of moisture content, below a predetermined level,remaining in the clothes and are a function of the electricalconductivity through the clothes. Additionally, the signal is indicativeof bridging or contact time of the clothes with the electrodes. As aresult of those two characteristics the initial signals generated arenot continuous but they are intermittent. Accordingly, switch meansinterposed between the signal generating means and the mechanicalintegrating timer is provided for advancing the timer motor in responseto a signal generated and stopping advancement of the timer motor in theabsence of a signal. (The cam associated with the motor is carried bythe shaft of the motor or driven by a gear train such that it isadvanced at the same rate as the motor.) Advancement of the cam isbetween a first position wherein the cam cooperating with a cam followeris effective to initiate operation of the dryer and a second positionwherein the cam and its associated follower are effective to terminateoperation of the dryer.

Other objects and advantages of the present invention will become moreapparent when considered in view of the following detailed descriptionin which:

FIGURE 1 is a perspective view, partly broken away, of a domesticclothes dryer incorporating the invention;

FIG. 2 is a cross-sectional view on the line IIII of FIG. 1;

FIG. 3 is a schematic wiring diagram incorporating the invention;

FIG. 4 is a top plan view of a sensor incorporated in the invention;

FIG. 5 is a side elevational view of a sensor pick-up incorporated inthe invention; and

FIGS. 6-8 represent a set of curves illustrating functionalcharacteristics of the invention.

Referring to the drawings, especially FIG. 1, reference character 10designates generally a domestic clothes dryer comprising a metallicclothes receptacle or drum 11 having a generally cylindrical shapeincluding an imperforate annular wall 12 and a perforate rear wall 13opposite a front wall 14. The front wall 14 has an opening 16 providingaccess to the interior of drum 11 for insertion or removal of clothes.

A bearing structure 17 journalled in the rear wall 13 and a peripheralflange 18 framing the opening 16 serve to support the drum 11 forrotation about a substantially horizontal axis within a cabinet 15. Thedrum is rotated by means of a conventional motor 19 through a flat drivebelt 21 encircling the annular wall 12 and a pulley 22 fixed to one endof the output shaft of the motor 19.

An impeller means 23 including blades mounted on the other end of themotor output shaft serves to circulate moisture removing air through theclothes and out of the dryer. The circulating air may be heated by meansof an electrical resistance heater 24 as the air is induced thereacrossby the impeller means 23, After being warmed by the heater 24 the airthen flows through the perforate rear wall 13, the clothes in the drum11, through a perforate rear panel 26 of the dryer door structure 27,through lint trap 28, front air duct 29, through the air impeller means23 and out of the dryer through an exhaust duct (not shown).

To provide the user with a choice of operation, therefore, with heat orwithout heat, a manually operable selector switch 31, connected in acontrol circuit 30 (illustrated schematically in FIG. 3), is adapted toconnect a power supply line L with a conductor L to place 230 voltsacross the heater 24. Alternately, the switch 31 is adapted to connectthe supply line L with a neutral conductor (N) to place 115 volts acrossthe heater 24. The dryer 10 may be operated without heat by placing theswitch 31 in the No Heat position which as can be seen moves the heaterfrom the circuit 31.

Mounted on an inner surface 32 of the annular wall 12 are a plurality ofclothes tumbling vanes 33, made from any suitable insulating material,for example, phenolic. There are preferably three such vanes and theyare preferably equally spaced one from the other.

Secured to the inner surface 32 partially subadjacent each of the vanes33 is a sensor structure 34 in the form of a printed circuit comprisingan insulator board 36 and two sets of electrical conductors orelectrodes 37 and 38. Each sensor 34 is secured to the annular wall 12by means of metal fasteners 39 and 40. The head of the fastener 39contacts the electrode 37 and the metallic drum 11 and is, therefore,effective in grounding the electrode 37 to the cabinet 15 of the dryer10 through the drum 11 and the bearing structure 17. The fastener 40comprises a screw 41 and a speed nut 42, the latter being in goodcontact with the electrode 38 and the former being suitably insulatedfrom the drum 11 by means of an insulator bushing 43.

The head of each of the screws 41, of which there are three, projectsoutwardly from the annular wall 12 and contacts a continuous metal band44 supported on the annular wall of the drum 11. The band 44 isinsulated from the drum by means of a felt pad 46 suitably bonded to thedrum 11 and disposed intermediate the band and the drum.

A sensor pick-up structure 47 (see FIGS. 1 and is mounted, by means ofan insulating bracket 48, to a flange 49 of the cabinet 15 such that acarbon brush 51 carried by a spring arm 52 engages the band 44. Thespring arm 52 is provided with an electrical terminal 53 for connectingthe sensor pick-up 47 to the control circuit 30 by means of anelectrical lead 54.

It will be understood that the electrodes 37 and 38 of any one of thesensor structures 34 are so positioned as to be simultaneously bridgedby clothes 55 tumbling in the drum 11 thereby providing a current flowpath from the latter to the former, the latter being supplied withelectrical energy from the power supply lead L through a resistor 57 theresistance valve of which may be normally varied by the user for apurpose which will be discussed hereinafter, in conjunction with a dampdry cycle of operation. The clothes 55 together with the electrodes 37and 38 constitute a variable resistor, or load sensing element, theresistance or conductivity of which is a function of the moisturecontent in the clothes. Therefore, when the moisture content is high theresistance is low and conversely when the moisture content is low theresistance is high.

A timer motor 58 indicated schematically in FIG. 3 carries a generallycircular cam structure 59 on the output shaft thereof. The cam structure59 is provided with a high portion 61 constituting the major part of theperiphery thereof and an indented portion 62 having a pair of steps 63and 64. The cam 59 is adapted to be normally positioned by the operatorby means of a program control knob 66 associated with an indicia bearingdial 65 carried by a back control panel 67. When the control knob 66 ispositioned by the operator a cam follower 68 rides on the high portion61 and is cammed thereby to effect closure of a first pair of contacts69 and 70 which completes a circuit from L to N through the motor 19 andto ground through the variable resistor 57 and the clothes 55.Simultaneously, the cam follower 68 effects closure of a second pair ofcontacts 71 and 72 thereby completing a circuit from L to L or N throughthe heater 24, that is if the circulated air is to be heated, otherwise,no circuit will be established through the heater when the switch 31 isin the No Heat position.

The timer motor 58 is preferably an AC sixteen pole hysteresis typesynchronous motor rated at 2.5 watts, 125 v. as marketed byInternational Register Company. In accordance with the present inventionit is desired that operation of the motor 58 be delayed initially,immediately following closure of the contacts 69 and 70, consequently,it is connected in series with a half wave rectifier or diode 73 and,therefore, will only operate upon firing of a thyristor or controlledrectifier 74 which bypasses the diode 73 in the oppostie polarity. Anexample of a suitable thyristor is type TSW23C (manufactured by theTransitron Co.) rated at 200 ma. with a gate sensitivity of 0.4 ma. Thegate 76 of the rectifier 74 is connected to the electrode 38 through avoltage sensitive switch herein illustrated as a neon lamp or glowdischarge tube 77. Such a device is marketed by the Signalite Co. undertype No. A-173-A. As is well known in the art such devices arenonconductive until a predetermined break down voltage is impressedthereacross. With such an arrangement the rectifier 74 is fired onlywhen the voltage across the electrodes 37 and 38, which with the clothes55 constitute one leg 56 of a voltage divider consisting of the variableresistor 57 and the former, reaches the firing voltage of the neon lamp77. When the clothes are wet, the resistance and, therefore, voltageacross the electrodes is low, consequently, a predetermined amount ofmoisture, for example, 80%, must be removed to raise the voltage acrossthe electrodes 37 and 38 thereby changing the divider ratio the requiredamount for firing the neon bulb 77.

Theoretically, the design of the electrodes and sensor pick-up may besuch that there would be enough stray capacity to fire the thyristor 74,however, a capacitor 78 connected across the electrodes 37 and 38 servesto store sufficient energy to fire the rectifier 74. A 220 pf. capacitorwas satisfactorily rused in practicing the present invention.

A diode 81 protects the gate 76 against reverse polarity. A resistor 79is provided to turn off (thyristor) in the absence of a firing signal.Other protective devices, shown schematically in FIG. 3, comprise anexhaust air thermostat 82 serving to control the general air temperaturein the dryer, and a safety thermostat 83 adapted to monitor the inletand temperature in the vicinity of the heater 24 and to preventoverheating of the apparatus.

It will be appreciated that during a cycle of operation, of the dryer10, the moisture level at which firing of the neon lamp 77 takes placecan be either raised or lowered by adjusting the variable resistor 57 bymeans of a dampness control knob 84 having indicia 85 indicative ofdegree of dampness. This changes the divider resistance ratio such thatthe voltage to the neon lamp 77 is either higher or lower for any givenmoisture. The higher the moisture at which the firing voltage of thelamp bulb 77 is reached the more moisture will be left in the clothesaccording to the degree of dampness and as indicated on the scale 85.

It will be readily understood by those skilled in the art that in lieuof using variable resistance for controlling dampness variable time inthe form of differential increments of distance on the surface of a camassociated with the timer motor 58 may be employed.

To illustrate the operation of the present invention, reference may behad to FIG. 6 wherein a graph 86 depicts the relationship of the voltagedrop across the electrodes 37 and 38 as an electrical signal generatedthereby and occurring during a cycle of operation of the dryer 10. Astraight line curve 87 represents the firing voltage of the neon bulb77. As will be apparent from the graph 86, during the early part of thedrying cycle when the clothes are very wet, the voltage across theelectrodes 37 and 38 is low and fairly smooth, but as the clothes beginto dry, the moisture becomes more uneven and the clothes load lightensthereby producing a noisy signal with ever increasing periods of highvoltage (i.e., voltage which exceed the firing voltage of the neon bulb77 as represented by the straight line 87) until the voltage drop acrossthe electrodes 37 and 38 finally levels off above the firing voltage ofthe neon bulb 77.

Since the controlled rectifier 74 is fired, thereby advancing the timermotor, only during the periods when the voltage drop across theelectrodes 37 and 38 exceeds the firing voltage of the neon lamp, therun-out or percent on time of the timer motor 58 is inverselyproportional to the contact time of the moist portions of the clothes 55with the electrodes. This characteristic of the invention is illustratedin FIG. 7 by a curve 88 representing percent contact time of the moistportions of a relatively large load of cothes with the electrodes versuspercent on time" of the timer motor with respect to time. As indicatedby the flat or horizontal portion of the curve 88, the clothes 55 areinitially very wet, consequently, the wet clothes contact the electrodes37 and 38 100% of the time. Once some of the moisture has been removedthe contacting of the electrodes by the wet clothes becomes less andless as indicated by the sloped portion of the sensor 88. It should beapparent that with relatively smaller loads of clothes, the contact timewill be somewhat less than 100% of the time. Consequently the presentinvention compensates the load size.

Another way of illustrating the run-out characteristic of the timermotor 58 is by a curve 89 which is a plot of timer run-out or on timeversus time. As can be seen on the first portion of the curve (noslope), the clothes being very wet and the contact time very high, thetimer motor does not run. When this foregoing condition exists no signalis generated. As the clothes become dryer and the contact time asrepresented by the second portion of the curve 89 (very shallow slope)the voltage exhibited across the electrodes 37 and 38 intermittentlyexceeds the firing voltage of the neon bulb 77 but does not remain abovethat level. Once this voltage or signal exceeds the firing voltage andremains at that level as represented by the third portion of the curve89 (i.e., very steep slope) the timer motor 58 remains energized andfunctions as a straight time run-out type of motor.

It will be understood that each time the timer motor 58 is advanced as aresult of a signal generated by the sensors 34, the cam 59 is advancedbetween contact closing and contact opening positions. In other wordsthe cam advances between a point on the high portion 61 of the camcontacted by the cam follower 68 and the step 64 wherein both sets ofcontacts 69, 70 and 71 and 72 are opened to terminate operation of thedryer. It should therefore, be appreciated that the cam structure 59 isstoring or mechanically integrating the electrical signals generated bythe sensor structure 34.

Since numerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings, shall beinterpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In fabric drying apparatus including a fabric sup porting drum andmeans for rotating said drum to tumble said fabrics, control structurecomprising:

means for generating signals indicative of the condition of saidfabrics,

signal integrating means operable between a first condition forinitiating operation of said drum rotating means and a second conditionfor terminating operation of said drum rotating means,

and means responsive to said signal generating means for progressingsaid signal integrating means from said first condition to said secondcondition,

said generating means generating electrical signals and said integratingmeans being electromechanical,

said electromechanical integrating means comprising an alternatingcurrent motor and cam means supported for rotation thereby,

rectifier means in series with said motor, said means responsive to saidsignal generating means comprising a bistable element connected to saidmotor such that it bypasses said rectifier means in the oppositepolarity.

2. Structure as specified in claim 1, wherein said signal generatingmeans comprises sensing means supported in said drum and voltagesensitive switch means.

3. Structure as specified in claim 2, wherein said sensing meanscomprises a plurality of electrodes adapted to be bridged by the fabricsin said drum and said bistable element comprises a thyristor having itsgate connected to said voltage sensitive switch means.

4. In a fabric dryer including a fabric containing drum and means forrotating the drum during a complete cycle of operation, means forcontrolling at least a part of said cycle of operation, said controlmeans comprising:

signal generating means,

integrating means,

and means responsive to said signal generating means for renderingoperable said integrating means,

said generating means generating electrical signals and said integratingmeans manifesting the integrated signals as a mechanical displacement,

said integrating means comprising an alternating current device and saidmeans for rendering said integrating means operable comprising a halfwave rectifier connected in series with said alternatmg current deviceand a bistable device connected to said alternating current device suchthat it bypasses said half wave rectifier in the opposite polarity.

5. Structure as specified in claim 4, wherein said signal generatingmeans comprises sensing means and voltage sensitive switch means thetriggering voltage of which serves to create a signal each time saidtriggering voltage is sensed.

6. Structure as specified in claim 5, wherein said sensing meanscomprises at least one set of electrodes supported in the drum andadapted to be bridged by the fabrics in said drum and said bistabledevice comprises a thyristor controlled rectifier having its gateconnected to said voltage sensitive switch.

7. Structure as specified in claim 6, wherein said voltage sensitiveswitch means comprise a glow discharge tube.

8. Structure as specified in claim 7, for manually varying the durationof noncontrolled part of the cycle of operation.

References Cited UNITED STATES PATENTS 3,248,799 5/ 1966 Worst 3453 XR3,248,800 5/1966 Pierce 3453 XR 3,324,568 6/1967 Nelson et al. 34-45FREDERICK L. MATTESON, 111., Primary Examiner.

A. D. HERRMANN, Assistant Examiner.

